Methyl cresyl or xylyl s-alpha aralkyl dithiophosphates



United States Patent 3 Claims. (Cl. 260-964) This is a division .ofapplication Ser. No. 153,201, filed No. 17, 1961 now abandoned.

This invention relates to motor fuels characterized by their ability tosuppress surface ignition in the operation of internal combustionengines. More particularly, the invention provides an improved motorfuel which is effective in suppressing surface ignition or preignition.

Current emphasis on high compression ratios and other high-performancedesign features in gasoline engines of the internal combustion type hascreated a situation where random knock from surface ignition, oftenreferred to as preignition, has become a limiting factor in enginedesign and operation. Knock induced by surface ignition appears to be aresult of the use of organo lead compounds, particularly tetraethyllead, as the anti-knock agent in high octane number fuels. When leadedmotor fuels are burned in internal combustion engines, deposits ofcarbonaceous material and lead salts are continuously formed on thecombustion chamber walls. Apparently surface ignition, that is, theignition of the fuel-air mixture either before or after passage of thespark, is caused by glowing of carbon in the deposits. It is generallybelieved that the presence of lead compounds in the deposits causes thecarbon to glow at a significantly lower temperature than the glow pointof carbon alone.

It is well known that the addition of certain organic compounds ofphosphorus, such as tricresylphosphate, to leaded fuels results inreducing surface ignition. Unfortunately, phosphorus compounds varywidely in eifectiveness, and those that are most effective often havethe undesirableproperties of lowering the octane number of the fuel aswell as increasing the octane requirement of the engine. With petroleumrefiners spending millions of dollars annually to raise the octanenumbers of premium motor fuels, any substantial decrease in octanenumber is of course intolerable. And, by the same token, the refinercannot provide a fuel that will itself aggravate the octane problem.

In accordance with the invention, an additive for use with leaded motorfuels has not been discovered which is extremely effective in reducingsurface ignition or preignition, yet whenemployed'in propen'qumtities,does not substantially reduce the octane number of thefuel or increasethe octane number requirement (0R1) of wherein n is 1 or 2 and X s amononuclear aralkyl radical having from 7 to about 15 carbon atoms, areoutstanding preignition suppressant additives when incorporated intoleaded gasolines in an amount sufficient to provide a mol ratio ofphosphorus to lead of from about 0.01 to about 1.0. Preferably, themolar ratio of phosphorus to lead (MR P/Pb) is in the range of0.02-0.30.

It has further been discovered, contrary to experience with many otherorganic compounds of phosphorus, that the inventive additives do notreduce oxidation stability of the gasoline, and hence do not increasethe tendency of the motor fuel to form gums in storage. In addition,they do not cause fuel induction system deposits nor do they causesticking of engine intake and exhaust valves.

The motor fuel of the invention may contain tetraethyl lead equivalentto a concentration of from about 0.5 ml. to about 5 ml. or more pergallon of the hydrocarbon motor fuel; the concentration of tetraethyllead may be varied as is usual with the engine and its use.

The hydrocarbon component which constitutes the base of the fuel willpreferably be gasoline but may be any other combustible liquid ofsuitable volatility commonly employed as fuel for internal combustionspark ignition engines, including paraffinic, naphthenic and aromatichydrocarbons, pure hydrocarbons such as isoctane, and mixtures ofisoctane with other suitable liquid hydrocarbons. These fuels may bederived, in whole or in part, by distillation of crude oil, catalytic orthermal cracking of gas oils, alkylation of isoparaffins with olefins,polymerization of olefins, etc. The boiling point of such fuels shouldbe in the range of about 80 .F. to about 500 F. and preferably in therange of about 90 F. to about 420 F. Motor fuels may also containanti-oxidants, stabilizers, dyes, anti-icing agents, halogen-type leadscavenging agents and/or other compounds which are commonly employed inleaded motor fuels.

There can also be provided, in accordance with the invention, anadditive concentrate suitable for incorporation into leaded motor fuelswhich contains a substantial amount (1 l00%) of the above describedthioester of disubstituted thiophosphoric acid. Thioester concentrationsof 5-85 |wt. percent are preferred. The additive concentrate may alsocontainan inert solvent, such as a refined hydrocarbon oil, and alsodesirable amounts of tetraethyl lead (to provide an MR P/Pb in the rangeof 001 1.0), halo-hydrocarbon lead scavenging agents, dyes,

and the like.

. phorus pentasulfide (P 8 to form a dithiophosphoric the engine.Specifically, it has now beendiscovered that 1 certain thioesters'ordithiophosphoric acid, herein sometimes referred to as the methyl cresyland methyl xylyl S-ot-phenylethyl dithiophosphate, having the formulaCHO S acid, and then reacted with an olefin of the radical (X) to beintroduced. It will be appreciated that amounts of other materials, e.g.the dimethyl or the dicresyl compounds will be formed, but these alsoappear to be excellent additive constituents. Typical examples ofappropriate cresols include p-cresol and commercial m-cresol andp-cresol mixtures, as well as o-cresol. Commercial xylenol is also quitesatisfactory.

It is preferred, for reasons of convenience and economy, to react thedithiophosphoric acid with an olefinic hydrocarbon having up to 15carbon atoms per molecule to form the inventive additive. As previouslymentioned, the X group is aralkyl, and accordingly the olefinichydrocarbon can be any compound which affords such group.

-. Among the suitable compounds which can form the X group of thedefined formula are styrene, a-methyl styrene, dimethyl-oc-methylstyrene, p-t-butyl styrene, and other aralkenes of 8-15 (more desirably8-10) carbon atoms. Using the styrenes, it is believed that the sulfuratom attaches to the carbon atom of the styrene.

As specific embodiments of the invention, the following examples aregiven. It is to be understood that these are by way of illustration onlyand are not intended as a limitation of the invention:

Example I This example illustrates the manner of preparing the inventiveadditives. For the preparation of methyl xylyl- S-a-phenylethyldithiophosphate, the following ingredients are used:

Ingredient Wt, g l Moles (1) Methanol 39 1. 2 (2) Commercial xylenol a A146 1.2 (3) Phosphorus pentasulfide. 111 0. (4) Styrene 124 1.2 (5)Solvent-extracted SAE-SW motor 0 88 Example II The preparation of methylp-cresyl S-a-phenylethyl dithiophosphate, the procedure of Example I isfollowed, except that 1.2 mols of p-cresyl alcohol is substituted forthe xylenol.

Example III In a manner similar to that of Example I, but with acommercial mixture of p-cresyl alcohol and m-cresyl alcohol replacingthe xylenol on a 1:1 molar basis, is carried out the preparation ofmethyl m-p-cresyl S-a phenyldithiophosphate.

Various phosphorus additives were tested in an engine operated todetermine surface ignition suppression effectiveness. This engine is asingle cylinder, CPR-L head engine, having a 7 to 1 compression ratio.Typical operating conditions for surface ignition or preignition studiesare as follows:

Test duration, hours 50 Coolant temperature, F. 148 Oil temperature, F.160 Air to fuel ratio 13/1 For this test the engine is cycled asfollows:

CYCLE CONDITIONS Time, sec 45 135 R.p.n1 600 900 Load None Full Surfaceignition prevention effectiveness was determined using a premium fuelhaving 3 cc. of TEL per gallon (in the form of commercial motor mix, andincluding scavengers) and incorporated therewith the inventive additiveand other phosphorus compounds.

EFFECTIVENESS IN SUPPRESSING SURFACE IGNITION CFR-L HEAD ENGINEConcentration, MR P/Pb The test data in the above table demonstrate thesuperiority of the present additive over other phosphorus compounds withrespect to surface ignition control. It will be noted that the additivemay be employed at onehalf to one-fourth the concentration of hithertowell know preignition suppressants.

It was previously indicated that a major advantage of the inventiveadditive is in its ability to be incorporated into high octane gasolineswithout substantially reducing the octane number of said gasolines. Todemonstrate this, tests were made in a CPR-L head engine at variousconcentrations of various concentrations of several additives in a 97-99octane number motor fuel, containing 3.0 cc. TEL per gallon. Thefollowing results were observed.

OC'IANE NUMBER DEGRADATION Concentration, MR l/Pb Additive Methylp-cresyl phenylothyl dithiophosphate Methyl rn-p-cresyl phenylethyldithiophosphate (Diisopropyl dithioshosp'noric acid) INDUCTION PERIODConcentration, MR P/Pb Additive Methyl p-cresyl phenylethyldithiophosphate 640 440 445 Methyl m-p-eresyl phenylethyl thiophosphate800 860 900 The additives were also tested for equilibrium octaneperformance in a 1953 Oldsmobile V-8 engine having special 10:1compression ratio heads, under the following conditions:

Speed, r.p.m. 1500 Load, BHP 9.5 Coolant temp, F. 175 Oil temp, F 165Air-intake temp., F. 100 Air-intake temp, F. 100 Spark advance, BTDC 11Once each hour the engine was operated at full-throttle, 1500 r.p.m.80BHP for 15 seconds. The equilibrium octane requirements and octanerequirement increase (ORI) of the engine were determined after hours ofoperation and are shown below. Superiority of the inventive compoundsover their adjacent homologue, phenyl methyl S-a-phenyl ethyl thiophsphate is particularly noted.

OCTANE REQUIREMENT INCREASE ISO-Hour Octane Rqmt. Power Additive Cone,Loss,

MR P/Pb percent Start End R1 None 101 115. 14. 5 Methyl p-cresylpheuyletliyl dithiophosphate 0.13 100 105 5 6. 5 Methyl m-p-cresvlphenylethyl dithiophospha 0. 13 100 106.0 6.0 0.13 100 104. 5 4. 5 3. 50.13 100 105. 5 5. 5 0.13 100 *114 14 3.6

*144 Hours.

The additives of Examples II and III were exposed to 15 AIR JET thecopper strip test, which consists of placing a clean copper strip in asample of motor fuel containing the ad- Additive Concentration, MRditive at 122 F., and examining the strip after three hours. Atconcentrations of 0.13 and 0 .33 MR P/Pb, the 0 i strips had the samegood color as the blank (zero ad- Methyl presyl phenylethyl dithiodltlveconcFPtratlom' phosphate 2.1 2.5 3,5

The additives also exert a powerful action on mamtain- Methylm-p-oresylphenylethyl dithioohosphate 0.4 1.0 1.6 mg spark plugs inclean, unfouled condition. In tests on Melthyl xylyl phenylethyl dithman Oldsmobile engine, the followmg results were obhos hate- 3.5 served:

The percentages given herein and in the appended L SPARK P UG LIFEclaims are weight percentages unless otherwise noted.

While the invention has been described by reference to Hours BeforeAdditive Cone, Fouling specific embodiments thereof, the same are givenby way MR of illustration. Modifications and variations will be ap- SetA Set B parent to those skilled in the are.

We claim: None 24 1. Methyl cresyl and methyl xylyl S-oc aralkyldithiolvl'efihyllp-eresylphenylethyldithio- O 13 150 150 phosphates.

osp a e r Mgthyl m-p-cresyl phenylethyl 13 96 63 75 30 2. Methyl CI'eSYlS-Ct dlthlophosphate.

dithiophoaphate 0. Methylxylylphenylethyl dithio 3. Methyl Xylyl S aphenylethyl dithiophosphate.

phosphate References Cited UNITED STATES PATENTS 40 As shown in thetable below, the inventive additives pass the air jet gum test of ASTMD38l, with respect to total gum formation. Not more than 4.0 mg. of gumis permissible in a satisfactory motor fuel.

3,113,005 12/1963 Gilbert 4469 CHARLES B. PARKER, Primary Examiner. A.H. SUTTO, Assistant Examiner.

1. METHYL CRESYL AND METHYL XYLYL S-A ARALKYL DITHIOPHOSPHATES.